Part 3—Analyze Earthquake Data
Step 1 –
Map Earthquake Data Using Latitude and Longitude Coordinates
- Choose View > Add Event Theme to map the earthquakes from the two files you created in Part 1 (i.e., Sig_Big_eq.csv and Last_year_eq.csv). Navigate to where one of the files is located. Then select the Longitude field for the X field and the Latitude filed for the Y field. If possible, change the Output Directory to /ESRI/AEJEE/Data/Earthquake and click OK. Repeat the procedure for the second file.
- Choose View > Add Event Theme to map last year's earthquakes using latitude and longitude coordinates.
- The Add Event Theme window opens. Click the folder to the right of the Table field and navigate to where the file for last year's earthquakes is located. Select the file by highlighting it and then click Open. Next, select the Longitude field for the X field and the Latitude field for the Y field and click OK. The Output directory tells where the new shape file will be created. If possible, change this location to /ESRI/AEJEE/Data/Earthquake. This way the new files that are created by AEJEE will end up in the same folder as the rest of the Earthquake data.
- A new layer, 2006eq, (in this example, your layer will be different) is created and added to the Table of Contents. The layer is turned on so that the earthquakes are displayed in the View.
- Repeat the procedure for the Sig_big.csv file to add those earthquakes to the file in a new layer.
Step 2 –
Turn Layers On and Off, Adjust Their Colors, and Rearrange Their Positions to Compare Earthquake Distributions
- When new data is added, AEJEE randomly selects a display color. Check to see that the two new point themes (Last_year_eq.csv and Sig_big.csv) are displayed in contrasting colors. If necessary, change the color of these layers. Right-click on the PC or control-click on the Mac on a layer's name in the Table of Contents. Then select Properties... Change the style, color, or size of the symbol from the Symbols tab in the Properties window. Click OK to close the Properties window and see the changes take effect on the map.
- Right-click or control-click on a layer's name in the Table of Contents. Then select Properties...
- The Properties window opens. Click the Symbols tab.
- Choose a color from the drop-down menu.
- Once you have selected a new color, click Apply to change the color of the symbol. Then click OK to close the Properties window.
- This is what the map looks like with 2006eq symbolized in green and Sig_big symbolized in blue. Your map may look different.
- Right-click or control-click the name of the layer containing last year's earthquakes. Then select Attribute Table. Scroll down to the bottom of the table to find out how many earthquakes with a magnitude of 5.0 or greater occurred in the past year.
- Right-click or control-click on the name of the layer containing last year's earthquakes. Then select Attribute Table.
- Scroll down to the bottom of the table to find out how many earthquakes occurred in the past year. (If you chose a different year or search setting, your number will vary from the one circled below.)
- Turn off last year's earthquakes and observe the Sig_Big layer. This layer maps "big" earthquakes ranging from the earliest recorded events to the most recent.
Uncheck the box in front of the most recent Earthquake layer name. (In the example pictured below, the most recent year is 2006eq.)
- How does the distribution of these earthquakes compare to the others?
Take a look at the Mid-Atlantic Ridge.
Big earthquakes tend to be concentrated in places where tectonic plates are colliding, rather than pulling apart. Concentrations of big earthquakes surround the Pacific Ocean in a pattern often described as the Ring of Fire.
- Turn these themes on and off to get a sense of how they differ.
- Move the Plate boundaries layer (bounds), to the top of the Table of Contents.
Right-click or control-click the
bounds layer in the
Table of Contents. Then select
Move Layer > Move to Top.
This is what the map looks like with the Plate boundary layer on top.
- What type of plate boundary is associated with earthquakes that have a magnitude of 7.0 or greater?
The plate boundaries are where the plates are coming together (red: convergent boundaries), spreading apart (orange: divergent boundaries) or moving horizontally past one another (magenta: transform boundaries). The green represents an unknown boundary type.
Big earthquakes occur most frequently at convergent plate boundaries.
Step 3 –
Create a Query and Set a Buffer to Characterize The Distribution of "Big" Earthquakes
As you discovered, most "big" earthquakes are concentrated at convergent plate boundaries. It is possible to characterize a risk zone using a GIS. For example, through querying and buffering, we can find out how many magnitude 7.0 or greater earthquakes have occurred within a specified distance of a plate boundary.
- Turn off last year's earthquakes, but make sure the Sig_big earthquake layer is on.
To turn off last year's earthquakes, uncheck the layer. Check the
Sig_big earthquake layer to turn it on.
- Select the convergent plate boundaries by querying the bounds layer for margin type.
- Click on the bounds layer to make it active.
- Then click the Query Builder...
button. In the Query Builder window, type the following expression into the input field: (MARGIN_TYP = 'Convergent').
- Click Execute.
- Here is what the map looks like with the convergent plate boundaries highlighted.
- Click the Buffer
button, then, in the Buffer window that opens, set the Buffer Distance to 100 and the Buffer Units to Miles. Check "Use buffer to select features from this layer" and select the Sig_Big_eq layer. Then click OK.
- Click the Buffer
button and in the Buffer window that opens, set the Buffer Distance to 100 and the Buffer Units to Miles. Check "Use buffer to select features from this layer" and select the Sig_Big_eq layer. Then click OK.
- Here is what the map looks like with a 100 mile buffer set around the convergent plate boundaries and with the intersecting earthquakes highlighted as well.
- Open the Attribute Table of the Sig_big layer to find out how many earthquakes were selected.
- Make Sig_big the active layer.
- Right-click (PC), or control-click (Mac), on Sig_big in the Table of Contents. Then select Attribute Table
- Scroll the Attributes of Sig_big to view the selected records. Note: depending on the data that you selected in Part 1, your number will vary.
- What percentage of big earthquakes occur within 100 miles of a convergent plate boundary?
Divide the number of earthquakes selected by the total number of earthquakes.
In this example, 588 of 1250, which equals 47% of big earthquakes occur within 100 miles of a convergent plate boundary. Depending on your data your percentages may vary.
- Click the Clear All Selections
button. Repeat the query and set the buffer again, but change the Buffer Distance to 200 miles.
- What percentage of big earthquakes occur within 200 miles of a convergent plate boundary?
Divide the number of earthquakes selected by the total number of earthquakes.
886 of 1250, which equals 71% of big earthquakes occur within 200 miles of a convergent plate boundary.
- Click the Clear All Selections
button.
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